As a man or woman stranded naked, freezing and starving on the shores of a mysterious island called ARK, you must hunt, harvest resources, craft items, grow crops, research technologies, and build shelters to withstand the elements. Use your cunning and resources to kill or tame the leviathan dinosaurs and other primeval creatures roaming the land, and team up with or prey on hundreds of other players to survive, dominate… and escape!

Actually, it’s not a MMO. But it seems to have a function like Minecraft’s one to open a world you created for friends to play with you. Using friends you know you can make this regular, and like Minecraft if you create a standalone world into a server you can open it to anyone and create a real server. So it is a “Private MMO” or something like this.
Hope it explains.
Source: I played games very like this (Stranded Deep and others).